Separation of molybdenum sulfide from copper sulfide with depressants

ABSTRACT

Molybdenum sulfide is separated from a molybdenite-containing copper ore concentrate by subjecting an aqueous pulp of the concentrate to froth flotation in the presence of a collector for molybdenum sulfide and a Nokes-type (e.g., arsenic trioxide/sodium sulfide) depressant for copper sulfide, the aqueous pulp being aerated with an inert gas to effect flotation of the molybdenum sulfide constituent of the pulp while maintaining the emf of the pulp above about minus 200 millivolts.

0 United States Patent [151 3,655,044 Delaney [451 Apr. 11, 1972 [54]SEPARATION OF MOLYBDENUM FOREIGNPATENTS on APPLICATIONS SULFIDE FROMCOPPER SULFIDE H 9,224 8/ l 919 Great Britain ..209/ l 66 WITHDEPRESSANTS [72] lnventor: John F. Delaney, Tucson, Ariz. Ch Abs ggz jzsem. tracts, [73] Assignee: The Anaconda Company, New York, NY. m n 5Anni, v 1962, pg. 5, 572

[22] Flled: 1970 Primary Examiner-Frank W. Lutter [2|] Appl. No.: 4,356Assistant Examiner-Robert Halper Attorney-Pennie, Edmonds, Morton,Taylor and Adams [52] US. Cl ..209/l67 [51] Int. Cl ..B03d l/06 [57]ABSTRACT 58 Field of Search ..209/166, 167 y num sulfid is separat d frm a molybdenite-comaining copper ore concentrate by subjecting anaqueous pulp of 5 m- Cited the concentrate to froth flotation in thepresence of a collector for molybdenum sulfide and a Nokes-type (e.g.,arsenic triox- UNITED STATES PATENTS ide/sodium sulfide) depressant forcopper sulfide, the aqueous pulp being aerated with an inert gas toeffect flotation of the 809.959 1906 Kllby ..209/ 166 molybdenum sulfideconstituent of the p p while maintaining the emf of the pulp above aboutminus 200 millivolts. 3,375,924 4/1968 Corbett ..209/ 167 6 Claims, 2Drawing Figures 5o V, .7 HM, r

i so i 1 C O 8 40 a w Q I S 30 Float Depressont Froth \0 Test lbs/TonMedium 20 A 5, 3 Air B 1.7 Air C |o.7 Air 3 o lo D |6.5 Air i L E 3. e Nz I F e .s N 2 l 0 l I O 2 4 6 8 IO l2 l4 l6 Time Minutes 0 CuDepression PATENTEDAPR 11 I972 SHEET 1 UF 2 E F D 90 0 V ..v. v in .W .ev

Float Depressonr Froih Tesr lbs/Ton Medium A 5.3 Air B 7.7 Air C :01 AirD we Air E 3.8 N2 \1 F 6 .5 N2 0 i i i O 2 4 6 8 l0 l2 l4 l6 TimeMinutes INVENTOR John F. Delaney ATTORNEYS SEPARATION OF MOLYBDENUMSULFIDE FROM COPPER SULFIDE WITH DEPRESSANTS BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to separationand recovery of molybdenum sulfide from copper ore concentratescontaining both molybdenum sulfide and copper sulfide by froth flotationin the presence of a collector for molybdenum sulfide and a depressantfor copper sulfide to effect recovery of a molybdenum concentrate in theflotation overflow and recovery of a copper concentrate in the flotationunderflow.

2. Prior Art Sulfidic copper ores frequently contain minor buteconomically significant amounts of molybdenite (M08 which, whenseparated from the copper ore, comprises an important source ofmolybdenum. By way of example, a typical low-grade copper ore maycontain about 1 percent copper sulfides and about 0.1 to 0.5 percentmolybdenum disulfide. Such copper ores are beneficiated by conventionalfroth flotation to obtain an ore concentrate containing typically about30 percent copper sulfides, if the ore is chalcopyritic, and about 1percent molybdenum disulfide, the molybdenite following the copperminerals in the flotation circuit. The molybdenite content of the copperore concentrate is then advantageously separated therefrom bydifferential flotation to obtain a molybdenum concentrate containing 90percent or more M08 As noted, sulfidic copper minerals and molybdeniteare normally floated by the same collectors. Therefore, in order toeffect differential flotation of molybdenite-containing copperconcentrates it is necessary either to depress the copper sulfides whilefloating the molybdenite content of the concentrate or to depress themolybdenite while floating the copper sulfide content of theconcentrate.

A process widely used in the industry for effecting the aforementioneddifferential flotation of molybdenite comprises conditioning an aqueouspulp of the molybdenite-containing copper ore concentrate with aconventional collector for molybdenum sulfide and with a Nokes-typedepressant for copper sulfide followed by froth flotation of theconditioned pulp with a conventional flotation machine to obtain amolybdenum concentrate as the flotation overflow (concentrate) and acopper concentrate as the flotation underflow (tailing). Nokes-typereagents are complex sulfidic compounds of phosphorus, arsenic orantimony and a caustic. They are available commercially from a number ofsuppliers, one such reagent being Anamol D which is a mixture of arsenictrioxide and sodium sulfide. Nokes-type copper depressants do notdestroy the ability of conventional copper collectors to collect andfloat copper minerals, they merely selectively mask or hinder thecollecting power of these collectors for copper minerals. It has beenfound that the amount of depressant in the pulp must be maintained abovecertain empirically determined levels to be effective. If the amount ofcopper depressant reagent present in the flotation pulp is insufiicientto be effective, either because an insufficient amount was initiallyused or because some of the depressant initially present has beenconsumed or lost, the collector employed to float both sulfide mineralsinitially will allow the copper minerals to refloat and efficientseparation of the two will not be obtained. Flotation plant operatorshave heretofore found that the amount of Nokes-type copper depressantrequired to insure efficient differential flotation is on the order offrom 15 to 20 pounds of depressant per ton of copper ore concentratesbeing treated. As Nokes-type reagents are relatively expensive, the

relatively large quantities of these reagents heretofore required toeffect efficient differential separation add significantly to the costof the molybdenum ultimately produced.

After an extensive investigation into the causes for high Nokes reagentconsumption I have discovered that if certain essential operatingprocedures and criteria are observed a relatively small amount ofNokes-type copper depressant is denite from sulfidic copper minerals.Specifically l have found that when a copper ore concentrate issubjected to conventional froth flotation in the presence of aNokes-type reagent differential flotation of the mineral values proceedsefficiently and effectively until a point is reached at which thereagent appears to lose, rather abruptly, almost all of its ability todepress copper minerals. At the same time the electromotive force (emf)of the flotation pulp, as measured by reference to a standard half-cell,progressively declines, the aforementioned abrupt loss in depressantability of the Nokes reagent becoming manifest when the emf of the pulpreaches the vicinity of minus 200 millivolts (-200 mv.). Both phenomenaappear to be the result of the progressive destruction or inactivationof the Nokes reagent which, in turn, appears to be due to the use of airor other oxidizing gases as the aerating medium in theconventional'flotation operation. Based on these findings anddiscoveries l have devised the improved process for the differentialflotation of molybdenite-containing copper ore concentrates that ishereinafter described.

SUMMARY OF THE INVENTION The improved process of the invention comprisesconditioning an aqueous pulp of copper ore concentrates containing bothmolybdenum sulfide and copper sulfide with a collector for molybdenumsulfide and a Nokes-type depressant for copper sulfide. The conditionedpulp is then subjected to froth flotation in which an inert gas (orgases) is employed as the froth producing medium to effect flotation ofa molybdenum concentrate in the flotation overflow and the recovery of acopper concentrate in the flotation underflow while maintaining the emfof the pulp above a predetermined value in order to maintain theeffectiveness of the depressant for copper sulfide. The amount of theaforesaid copper depressant in the flotation pulp should be sufficientto maintain the emf of the pulp above about 200 mv. when measured with aplatinum electrode with reference to a standard GP glass electrode-(calomel electrode). The froth producing gas should be one which willnot oxidize or react with the copper depressant and advantageously isselected from the group consisting of nitrogen, or the inert gases suchas helium and argon, or a mixture of these gases. I presently prefer toemploy nitrogen as the aerating gas, although specially treatedcombustion gases the flue gases containing only nitrogen and other inertgases may also advantageously be used.

BRIEF DESCRIPTION OF THE DRAWINGS DETAILED DESCRIPTION As previouslydescribed, sulfidic copper ores frequently contain minor amounts ofmolybdenum sulfides. Conventional ore beneficiation operations result inthe preparation of a copper ore concentrate that may typically containup to about 30 percent by weight copper sulfides (if the ore ischalcopyritic) and up to about 1 percent by weight molybdenite (M08 Themolybdenite is advantageously separated from the copper ore concentrateby differential flotation in which an aqueous pulp of the concentrate isconditioned with a conventional collector for molybdenum sulfide andwith a depressant for copper minerals, the conditioned pulp then beingsubjected to conventional froth flotation to obtain a molybdenum sulfideconcentrate as the flotation overflow and a copper sulfide concentrateas the flotation underflow. The copper depressant employed isadvantageously one of a variety of required to effect efficientdifferential separation of molyb- Nokes-type reagents. Nokes-typereagents were first described .,ing gas. The amount of Nokes-typereagent required to depress copper minerals effectively during suchconventional froth flotation operations has heretofore been detenninedempirically by plant operators to be in the order of from l5 to poundsof reagent per ton of copper concentrates being treated. As a result ofmy investigations 1 have found that when a non-oxidizing gas is used asthe froth producing gas in place of air, and when the electromotiveforce (emf) of the flotation pulp is maintained above a predeterminedvalue, the amount of Nokes-type reagent required to depress copperminerals effectively is reduced to about one flfth to one half of theamount heretofore required.

' Specifically, l have found when a copper ore concentrate isconditioned with a Nokes-type reagent and is subjected to conventionalfroth flotation using air as the froth producing gas that, after acertain period of time, the Nokes reagent rather abruptly loses itsability to depress copper minerals and as a result these minerals nowappear in the flotation overflow (the froth) as though no copperdepressant were present in the pulp. I have also found when using air asthe froth producer that the emf of the flotation pulp progressivelydecreases from a maximum initial value to a final value that closelyapproaches the emf of the unconditioned pulp. The length of time'thatthe Nokes reagent retains its ability to depress copper minerals dependsdirectly on the amount of reagent initially present in the pulp, and therather abrupt loss in the ability of the reagent to depress theseminerals appears to take place when the emf of the pulp reaches anempirically predetermined value. These findings indicate that, in thecourse of conventional froth flotation with air, Nokes reagents areprogressively decomposed or consumed until insufficient reagent remainsin the pulp to be effective.

When an inert gas that is non-reactive with respect to the highlyalkaline Nokes reagent is used as the froth producing gas, the emf ofthe flotation pulp remains substantially constant, and the Nokes-typereagent retains its ability to depress copper minerals, throughout theduration of the flotation operation. Moreover, when an inert gas is usedas the froth producing medium, a substantially smaller quantity ofNokestype reagent may be used as a copper depressant than is the casewhen air or some other oxidizing gas is employed as the froth producer.The non-oxidizing gases useful in the practice of the invention include,but are not necessarily limited to,

nitrogen; and other inert gases such as helium and argon; and.

various mixtures of these gases. One convenient source of this type ofgas is flue gas or combustion gas which has been cooled and cleaned toremove dust particles and treated to remove free oxygen, carbon dioxideand/or carbon monoxide therefrom.

The emf of the flotation pulp is determined by techniques that are wellknown in the art. in brief, the electrical potential of the pulp ismeasured by reference to the potential of a con- ,of the emf orpotential of the pulp will depend on a number of factors which includethe type and composition of the copper ore concentrate, the type'andconcentration of the Nokes reagent employed and the type of standardhalf cell with ,reference to which the emf of the pulp is beingmeasured. However, for a given ore concentrate, Nokes reagent and typeof standard half cell the emf of the pulp is essentially reproduciblefrom sample to sample. Moreover, in such cases the emf of the pulp atwhich approximate value the Nokes reagent appears to lose its ability todepress copper minerals is approximately the same from sample to sample,and this approximate emf value can be empirically predetermined for anygiven ore concentrate, Nokes reagent and standard half cell by knowntechniques. By way of example, when a chalcopyrite copper concentrateproduced from Twin Buttes ore is conditioned with Anamol D, acommercially available Nokestype reagent, the reagent appears to loseits ability to depress copper minerals when the emf of the flotationpulp decreases 20 to about -200 to 250 mv. when measured with a platinumelectrode with reference to a standard GP (calomel) glass electrode.

The following examples are illustrative but not limitative of thepractice of the invention.

EXAMPLEI A series of flotation experiments were performed on freshlyproduced Twin Buttes copper concentrates assaying approximately 31.9percent copper and 0.51 percent molybdenum to extract a molybdeniterougher concentrate by the use of Anamol D, a Nokes-type reagent, as thedepressant for copper minerals. A single portion of the ore concentratewas divided into four equal samples having an average weight of about740 grams. Each sample (herein referred to as Samples A, B. C and D) wasconditioned with the same collector for molybdenite and with a differentamount of the aforementioned Nokes-type depressant for copper. Theseconditioned flotation samples are set forth in Table l.

Each conditioned sample was then subjected to froth flotation in astandard laboratory flotation machine for a total 5 5 period of 16minutes using air as the froth producing gas. The

emf of the conditioned flotation ulp prepared from each sample wasdetermined just before he start of each flotation experiment andthereafter at two minute intervals throughout the duration of theexperiment. The flotation overflow (that is,

0 the froth) was also collected at two minute intervals and the mineralcontent thereof weighed and assayed. At the conclusion of eachexperiment the flotation underflow (that is, the tails) was collectedand the mineral content thereof weighed and assayed. The results ofthese four flotation experiments detta! enearrhal 991. Tht a olutevalue. n m o 65 a e s lf alabl 21 TABLE 2 Flotation rate tests A, B, Cand D show the efiectiveness of Anamol D (a type of Nokes reagent) atdiflerent. concentrations with respect to time and show, by Mv readings,the decomposition of Anamol D when using air as the froth producing gasWeight Cum. Assay products Cum. distrib. Mv readproducts percent ingafter grns. wt. Cu Mo Cu Mo flotation Mo rougher concts., minutes:

3.33 1s. 25 16.21 1. 93 70.11 -220 13. so 26. e3 1. as 10. s1 s9. 96-1eo 30.50 32, 2s 304 2 7332 94. 4s l Table 2 -Continued Weight Cum.Assay products Cum. distrib. Mv randproducts percent ing nitor gins. wt.Cu M Cu Mo flotation 133 48.10 33. 77" i 1080 46. 80 "96. 32 -120 14467. 30 34. 62 060 67. 87 07. 67 -100 107 81. 70 34. 64 048 83. 63 98. 46-90 44 87. 60 33. 14 064 89. 69 98. 80 80 14-16 20 90. 20 30. 88 070 92.30 99.11 70 316 rougher tails: 0-16 minutes- Test of sample B (7.66ibs./t. Anamol D": Mv reading at 0 time=-520 Mv) Mo rougher concts.,minutes:

0-2 26 3. 66 16.93 6. 89 1. 89 42.32 -380 12 6. 20 18.85 16. 04 2. 8687. 79 270 170 28. 50 30. 88 160 25. 39 94. 22 -'-190 201 66. 0 a 33.19046 64. 02 96. 41 -160 .126 73. 0 34. 73 036 72. 66 97. 48 -130 70 82. 634. 96 .038 83. 98. 10 -120 32 87. 2 36. 42 066 88. 02 98. 63 -100 14-1618 89. 6 34. 46 .072 90.68 98. 84 80 Mo Rougher Tails: 0-16 minutes I 7610. 4 28.58 .064 9. 32 1. 16

Test of sample C (10.7 1bs./t. Anamol D; Mv reading at 0 time=560) Morougher concts., minutes:

Test of sample D (16.51bs./t. Anamol "D; Mv reading at 0 time=610) Morougher concts., minutes:

0-2 1 8 1. 09 6. 92 18.42 23 39. 07 -'480 7 2. 05 10. 38 18. 02 64 72.63 -'470 6 2. 73 16. 64 9. 06 89 84; 62 -390 2 3. 00 16. 94 6. 61 1. 0387. 98 -330 2 3. 18 16.80 3. 37 1. 17 89. 77 -290 2 3. 66 13. 93 1165 1.29 90. 66 -260 13 6. 31 14.10 .330 2. 07 91. 80 -220 14-16 76 16. 70 30.80 066 12. 00 93. 12 190 Mo rougher tails: 0-16 minute 618 84. 30 33. 67042 88.00 6. 88

' EXAMPLE ll TABLES A second series of flotation experiments wereperformed on Sample Molybdlnilc Copper lnillal similar freshly producedTwin Buttes copper concentrates, 6 1e 5:22 ig st single portion of theore concentrate being divided into two 40 P a s equal samples (hereinreferred to as Samples E and F) having 5 5.27 4176 u an average weightof about 510 grams. Each sample was con- F 493 0.81 6.5 360 ditionedwith the same molybdenite collector and each with a different,relatively small, amount of Anamol "D, the Nokes- The emf of theflotation pulp was measured, and the flotation type copper depressant.These conditioned flotation samples are set forth in Table 3.

Each conditioned sample was then subjected to froth flotation in thesame laboratory flotation machine for a total period overflow wascollected and assayed, as in Example I. At the conclusion of eachflotation experiment the underflow was collected and assayed as before.The results of these two flotaof 16 minutes using nitrogen as the frothproducing medium. tion experiments are set forth in Table 4:

TABLE 4 Flotation rate tests E and F show the effectiveness of Anamol Dat relatively low concentrations when using nitrogen instead of air asthe froth producing gas Weight Cum. per-' Assay Products Cum. distrib.Mv readproducts cent wt. ing after gins. eonets. Cu Mo Cu Mo flotationTest of sample E (3.8 ib9./t. Anamol "D; Mv reading at startflotation=370) Mo rougher concts., minutes:

14-16 Mo rougher tails 0- Test of sample F (6.51bs./t. Anamol Mv readingat start iiotation= 360) Mo rougher comets, minutes:

. 3. 12 14-16 1 1 8. 14 Mo rougher tails: 016 minutes. 453 91.86 31.3902 96. 88 I 3. 97

1 Approximate. I N o assays.

The results of the flotation experiments described in Examples I and llare combined and are presented graphically in FIGS. 1 and 2 of thedrawings. FIG. 1 shows the effectiveness of various concentrations ofAnamol D" as a copper depressant with respect to time (duration offlotation) when air and when nitrogen are used as the froth producinggas. FIG. 2 illustrates the progressive decrease in the emf anddepressing effect of the Nokes reagent on copper minerals in theflotation pulp when air is employed as the froth producing gas ascontrasted with the relatively constant emf and the efiective depressionof the copper minerals in the pulp when nitrogen is employed for thispurpose.

Referring to FIG. 1, it is evident that, when the froth producing gas isair, the percent of copper depressed with respect to time is a functionof the amount or concentration of Nokes reagent initially present in theflotation pulp. Moreover, it is evident that for a certain length oftime, depending on the initial concentration of the Nokes reagent, thepercent of copper depressed is very high until, rather abruptly, thereagent appears to lose its ability to depress copper minerals,whereupon the percent of copper minerals depressed drops sharply. Incontrast to this, when the froth producing gas is nitrogen, the Nokesreagent retains its ability to depress copper minerals withoutappreciable deterioration throughout the flotation operation. ofparticular significance is the fact that when an inert gas is used asthe froth producer, the amount of Nokes reagent required to achieve andmaintain a very high degree of copper depression is markedly less thanthe amount required when air is employed as the froth producing gas.

Referring to FIG. 2, the contrast between the rapid decrease in the emfof the flotation pulp when air is used as the froth producer and therelatively stable emf of the pulp when Nokes reagent is apparent.

I claim:

1. The process for the separation and recovery of molybdenum sulfidefrom copper ore concentrates containing both molybdenum sulfide andcopper sulfide which comprises conditioning an aqueous pulp of thecopper ore concentrates with a collector for molybdenum sulfide and aNokes-type depressant for copper sulfide, and subjecting the conditionedpulp to froth flotation in which an inert gas that will prevent anyoxidation from occuring in the conditioned aqueous pulp is employed asthe froth producing medium to effect recovery of a molybdenumconcentrate in the flotation overflow and recovery of a copperconcentrate in the flotation underflow while maintaining the emf of theaqueous pulp above a predetermined value to maintain the effectivenessof said depressant for copper sulfide.

2. The process according to claim 1 in which the emf of the aqueous pulpis maintained above about -200 mv. when measured with a platinumelectrode with reference to a standard GP (calomel) glass electrode.

3. The process according to claim 1 in which the depressant for coppersulfide is a reaction product of two or more inorganic compounds, saidreaction product containing bivalent sulfur, a caustic cation and,combined therewith, an element selected from the group consisting ofphosphorus, aresenic and antimony.

4. The process according to clarm 3 m which the aqueous

2. The process according to claim 1 in which the emf of the aqueous pulpis maintained above about -200 mv. when measured with a platinumelectrode with reference to a standard GP (calomel) glass electrode. 3.The process according to claim 1 in which the depressant for coppersulfide is a reaction product of two or more inorganic compounds, saidreaction product containing bivalent sulfur, a caustic cation and,combined therewith, an element selected from the group consisting ofphosphorus, aresenic and antimony.
 4. The process according to claim 3in which the aqueous pulp contains a sufficient amount of saiddepressant for copper sulfide to maintain the emf of the pulp aboveabout -200 mv. when measured with a platinum electrode with reference toa standard GP (calomel) glass electrode.
 5. The process according toclaim 1 in which the non-oxidizing aerating gas is selected from thegroup consisting of nitrogen, freon, the inert gases and mixturesthereof.
 6. The process according to claim 1 in which the non-oxidizingaerating gas comprises nitrogen.